As Lady Lottie in TV's Any Human Heart, Emerald Fennell draws on her own refined background to great effect. But she longs for parts that stretch her
• Emerald Fennell as Lady Lottie in Any Human Heart
EMERALD Fennell is only 25 but already she's had a vision of herself at 50. Playing Lady Lottie, Matthew Macfadyen's first wife in Channel 4's adaptation of William Boyd's novel Any Human Heart, she had to let go of vanity. At the weekend you could watch her wearing prosthetic make-up to play a raddled older Lottie at her son's funeral. When she texted the picture to her boyfriend, he shot back: "Emerald, oh gosh, this is really not what I signed up for."
In the flesh, Emerald - daughter of top jeweller Theo Fennell - is stunning, with porcelain skin, cat-like eyes and a distracting mouth. Her hair, blonde for the part of Lottie, is dyed red when I meet her. She's wearing silver skull and snake pieces from her father's diffusion range, Alias, which is launched next month. "He'd probably prefer me to wear one piece chicly - but I chuck it all on!"
I ask if she minded playing a humourless, spoiled aristocrat in Any Human Heart when Hayley Atwell and Kim Cattrall - as Macfadyen's mistresses - got to vamp about in gorgeous outfits?
"It was so nice to play an unsympathetic character," she laughs. "Especially when those 1920s girls are usually portrayed as fragrant, cigarette-smoking types, lounging around. I think Lottie is more what that sort of girl would have been - not really caring about her clothes, forthright and bossy. It made far more sense that she's a little bit childlike and… not stupid… but socially awkward."
She feels sorry for Lottie - who makes a brave but doomed choice to marry a man from a different class. "She's a spoiled only child. She has a very intense relationship with her father. The director and I discussed it - it's almost bordering on incestuous and she can do whatever she wants. Then she meets this artistic, sexy man who has written a scandalous book and she really gets off on it."
Though she does mourn the fact that her first on-screen sex scene - where Lottie tries to seduce her husband to get pregnant again - ends so humiliatingly. "I get rejected in bed by Matthew Macfadyen, just the saddest day of my life! It's a particularly grim thing for a woman. Men, for some reason, are culturally used to the entire 'I've got a headache' thing. But for a man to physically push his wife off is mortifying. Mind you," she adds with a glint, "I like the fact she's a bit of a goer."
We meet at Fennell's flat in London. "Sorry, we had a dinner party last night," she apologises, leading me into the spotless kitchen. But Fennell is no empty-headed society girl.
After Marlborough College (also attended by Prince William's intended Kate Middleton a few years previously), she studied English at Oxford where she acted in university plays. There she was spotted by Lindy King of United Agents, who represents Keira Knightley.
"We were doing Nina Raine's play Rabbit," Fennell recalls. "Her father (Craig Raine] is a don and so he came to see a few rehearsals and gave us some tips. It was a great part because I was playing a really unpleasant bitch - a delusional, sexually incontinent nightmare, which was just the best thing ever. And Lindy fortunately saw through that."
Her first acting job was as one of Howard Marks's girlfriends in the film Mr Nice, where she lounged around in 1960s clothes and smoked a lot. Then she heard Channel 4 was making Any Human Heart. A huge fan of Boyd's book, she begged King to put her up for any role, no matter how small. "I would have said one word, just swept up in the background," she laughs.
She is certainly privileged. Her Old Etonian father is best-known for designing witty baubles - solid-silver lids for Marmite pots, sterling silver fish-and-chip sets - for Elton John. Keith Richards is a family friend. William Boyd has known Theo Fennell since the 1970s, which may have helped a little with the casting.
But there's no question Emerald is bright. And great fun. She was always the child putting on plays and showing off at dinner parties and describes "a life of constantly making an exhibition of myself". Age 15, she saw Rachel Weisz in The Shape of Things. "I was totally blown away and thought 'That's what I want to do.'" Her parents were supportive but insisted she got a proper education first. Her family has known turbulent times. In 2008 her father was ousted from his jewellery business for a year after an argument over strategy but now he's back in the driving seat, and profits are up. Her mother, Louise, recovered from breast cancer eight years ago.
In gaps between acting, she writes. She has finished a novel for young adults, and was commissioned to write a film script (co-produced by Madeleine Lloyd Webber). Called Chukka, it's a rom-com about a group of teenagers who fight the closure of their school by taking on the rich kids at polo. She is glad her father is not an actor. "You don't want that level of watchfulness. Your father going, 'I'm not sure I liked your speech in Hamlet.' F*** off, Dad! That would be so stressful. But they're very cool."
Her sister Coco has set up her own fashion label. "She wanted to do flirty, fun clothes for girls. Lovely dresses you can chuck on in the morning. The opposite of those backless, bandaged, studded, nipple-less catsuits that we desperately try to squeeze into," she hoots. "She's a very visual creature, which I think she gets from Dad."
She ice-skates, goes to the gym and "sobs on the treadmill" to keep fit.
While she doesn't applaud size zero -"It's easy for young girls to tip over from casual concern over fitting into tight jeans into full-blown obsession" - she knows looking good is part of her job.
With her curves and posh niceness Emerald is like a character out of an Agatha Christie novel. It would be interesting to see her play a role on the other side of the tracks. Casting directors, take note.
• The final episode of Any Human Heart is on Channel 4 on Sunday at 9pm